The present invention relates to a hologram laminate and a hologram label that are suitable for certification and forgery preventing purposes and also superior in graphical design function.
Holograms allow information to be recorded on the surface of a hologram layer or in the direction of the thickness of a hologram layer and also permit three-dimensional image recording and reconstruction. Further, holographic images have an appearance that cannot readily be obtained by other image forming means because they are represented by the interference color of light. Although the method of producing holograms is per se known, it is difficult to forge holograms because the production thereof requires a precise operation using optical equipment. Accordingly, holograms are used as labels for certifying that labeled articles are authentic, and also used to prevent forgery of ID cards, bank cards, etc.
Various holograms are known, for example, a relief hologram in which information is recorded on the surface of a hologram layer, and a volume hologram in which information is recorded in the direction of the thickness of a hologram layer. In addition, a composite hologram is known in which a volume hologram and a relief hologram are superimposed so as to be switchable from one to another, as disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 11-84995. The composite hologram allows image reconstruction by light diffraction even at an angle outside the reconstruction angle range of the volume hologram, thereby widening the range within which the reconstructed image is visible, and thus improving the graphical design function of the hologram. When such a hologram is bonded to an adherend as a label for certification by using a pressure-sensitive adhesive, the hologram layer is readily separable due to the difference in material between the hologram layer and the adherend and hence replaceable with another. Therefore, it is necessary to make it impossible to replace the hologram layer with another when the hologram is used as a label for certification.
Under these circumstances, Japanese Patent Application Unexamined Publication (KOKAI) No. 2000-194265 discloses a hologram laminate comprising an adherend, a hologram layer and a surface protective film. In the hologram laminate, a release pattern is provided between the surface protective film and the hologram layer, and a pressure-sensitive adhesive containing a coloring material is used to form a colored pressure-sensitive adhesive layer for forgery preventing purposes. Thus, when the hologram layer is separated, the colored pressure-sensitive adhesive layer is left on the adherend in a pattern corresponding to the release pattern. With this arrangement, a hologram laminate excellent in forgery preventing capability can be obtained. However, when the hologram laminate is used as a seal for certification, it is demanded that a pattern showing traces of separation of the hologram should be left even more clearly on both the adherend and the hologram label. In the hologram laminate disclosed in the above-described publication, however, the bond strength of the colored pressure-sensitive adhesive layer is so high that the pattern showing the separation of the hologram is unclear. Accordingly, the conventional hologram laminate is inadequate for certification purposes.
The present invention relates to a hologram laminate that allows traces of separation of the hologram to be clearly left on both the adherend and the hologram label and hence makes it possible to prevent reuse of the hologram and that is excellent in graphical design function and suitable for certification purposes. The present invention also relates to a hologram label used for the fabrication of the hologram laminate.